The Minnesota Pollution Control Agency said it plans to make preliminary recommendations by the end of February on whether a state standard meant to protect wild rice from sulfate discharges should be changed based on a stack of reports and data just released from a major study.

But the agency deferred drawing any immediate conclusions from the extensive field and laboratory research, which was conducted by scientists at the University of Minnesota’s Duluth and Twin Cities campuses. MPCA officials need to do more work to evaluate the research before they can recommend whether the sulfate standard should be changed, said Shannon Lotthammer, director of the MPCA’s environmental analysis division.

Minnesota limits sulfate discharges from mines and other sources into waters that produce wild rice to 10 milligrams per liter, based on research from the 1940s suggesting that higher levels can stunt development of the plants. Supporters of iron and copper-nickel mining have argued that the standard is obsolete, while the state’s American Indian bands fear any weakening could imperil a food source they consider sacred and central to their cultural identity.

The theory behind the overall three-year study is that higher concentrations of sulfates can harm wild rice plants when they’re converted into sulfides in the sediments where the plants grow. While the study summary says some of the reports on specific aspects of the research include data about sulfate and sulfide concentrations and their effects on wild rice, it would be “premature” to say whether they show that the standard should be changed.

“Each Study component uses a different approach to examine how sulfate might affect wild rice. The results of each component must be analyzed and integrated with the other components before any recommendations can be made about the standard,” the report said.

John Pastor, a UMD biologist who was the lead researcher, agreed with that assessment.

“People may think that whether the standard is correct or not is a simple yes-or-no question that is easily answered by the data. But it isn’t and never was because the transformations and cycling of sulfur in wild rice beds are complicated. That’s just the way Nature is,” Pastor said in an email.

The mining industry has argued that companies shouldn’t be required to invest large sums in sulfate treatment technology that might not be needed.

“We want to protect wild rice, but we believe that any standard for the level of sulfate in wild rice waters has to be based on science,” said Frank Ongaro, executive director of the industry group Mining Minnesota. “That’s what this study was supposed to do, so we’ll see what the agencies make of the results.”

Tom Howes, natural resources manager for the Fond du Lac Band of Lake Superior Chippewa Indians, who harvest wild rice in waters downstream from the state’s main mining area, said he hadn’t fully digested the reports and data and didn’t want to speculate on what the MPCA might conclude.

“I’d rather they were cautious than hasty. It’s an important study,” he said.

But Howes said a virtue of the current standard is that it was set conservatively, instead of close to a breaking point. “It’s protective. To me that’s a good standard,” he said.

The Minnesota Center for Environmental Advocacy will take a close look at the results, said Scott Strand, executive director of the group, which has defended the current standard.

“The burden is on the people who want to change it, not the people who think it’s appropriate where it is,” he said.

Lotthammer said there will be opportunities for public and expert reviews of the research, and there will be a formal public comment process if the MPCA decides there’s a scientific justification for changing the standard.